There has been well known antimicrobial zeolite which comprises a zeolite material whose ion-exchangeable metal ions are replaced with antimicrobial metal ions such as silver, copper and/or zinc ions as well as an antimicrobial composition containing the antimicrobial zeolite. In this respect, it has been known that an antimicrobial resin composition comprising a resin and such antimicrobial zeolite incorporated therein undergoes color change with the elapse of time. As a means for solving the problem that a conventional antimicrobial zeolite of this type undergoes a color change with time, there has been proposed a technique in which silver ions and ammonium ions are incorporated into zeolite (Patent Document 1 specified below).
The antimicrobial zeolite disclosed in this document is in fact a quite excellent antimicrobial agent since it is certainly excellent in its durability of antimicrobial properties observed when allowing it to stand in water or in the air and it does not cause any deterioration even when incorporated into in a resin through kneading operations.
The antimicrobial zeolite disclosed in this document does not suffer from any problem such that it may undergo any extreme color change under the usual use conditions, but it sometimes undergoes a color change with time under severe conditions, for instance, when it is exposed to intensive ultraviolet light rays over a long period of time. The zeolite does not lose its antimicrobial properties peculiar thereto even when it undergoes such a color change, but when adding the antimicrobial zeolite to a product, the latter may often result in discoloration and commercial value of the product may sometimes significantly be damaged depending on the kinds of the product.    Patent Document 1: Japanese Un-Examined Patent Publication Sho 63-265809.